Fill valves function to refill a tank or reservoir to a predetermined liquid level and then automatically shut off. Fill valves are used widely in toilet tanks. Many improvements in fill valves have eliminated the need for a ball cock used as a float that shuts off the valve when the water within the tank reaches the fill level. U.S. Pat. Nos. 3,895,645 issued July 22, 1975 and 4,180,096 issued Dec. 25, 1979 disclose fill valves that are compact and mounted at the bottom of the tank and are entirely submerged when the tank is filled. U.S. Pat. Nos. 4,574,826 and 4,646,779 issued on Mar. 11, 1986 and Mar. 3, 1987, respectively, disclose a fill valve which has the main valve mechanism mounted to be above the overflow level of the tank.
All four patents disclose diaphragm actuated fill valves in which the diaphragm is responsive to pressure in order to turn the main valve on and off. The 4,574,826 and 4,646,779 patents disclose a diaphragm which responds to air pressure within a control chamber. The main valve is positioned above the overflow level of the tank and is mounted on top of a stem section of the valve housing. As the water in the tank rises to an actuation pressure level outside the control chamber, the air is compressed by water rising in a downwardly facing open end of the control chamber, filling the control chamber to a response level that sufficiently compresses the air therein. All the teachings in the above mentioned patents are incorporated in this application by reference.
Commonly, toilet tanks use about two and a half gallons of water per flush. After the fill valve is properly adjusted to its correct height, the exact amount of water within the tank is not crucial for an adequate flush and any deviation due to differences in ambient air pressure or actual changes over time in the diaphragm or due to manufacturing tolerances of other fill valve parts will not significantly affect the flush. However, newer more water conserving toilet tanks offering over 40% reduction of water have been made that use approximately one and a half gallons of water. These low water consumption toilets are more sensitive to deviation in water levels. Differences as low as one cup of water can make a critical difference in obtaining an acceptable flush. As such it is more important to have a precise amount of water in the tank. It is important to accurately fill the tank after each flush and eliminate any deviations of water height due to ambient air pressure, other manufacturing tolerances of the diaphragm or other fill valve parts, or changes occurring over time to the toilet fill valve parts.
Furthermore, most toilet tank designs have a low profile wherein the water level drops only approximately an inch and a half from the fill level to the empty level. It is important that any actuation shut off device needs to be operable and recyclable with no more than the one and a half inch water drop available in most tank designs found in present low water consumption toilets.